1. Field of the Invention
The present invention relates to a an image developer, a process cartridge and an image forming apparatus for electrophotographic image forming processes in copiers, facsimiles, printers, etc.
2. Discussion of the Background
Conventionally, as disclosed in Japanese Patent No. 3320954, one-component image developer has been known, in which a non-magnetic or a magnetic toner (developer) included in a container is fed to a developing roller (developer bearer) with a toner feeding member (roller) formed of a foamed polyurethane, etc., an elastic member such as a metallic thin plate is pressed to the developing roller (developer bearer) to uniform a toner thereon, and an electrostatic latent image formed on a photoreceptor (image bearer) is developed with toner.
Recently, in compliance with color-oriented demands at offices, full-color image forming apparatuses appear. One of the full-color image forming apparatuses is a photoreceptor-of-four tandem image forming apparatus including four image forming units in which a yellow toner image, a magenta toner image, a cyan toner image and a black toner image are formed on each 4 photoreceptors with a powdery one-component developer (toner), and the images are sequentially transferred onto a receiving material to form a full-color image thereon.
However, the image developer in which a developer charging and layer forming part and a developer storing part are located in parallel as disclosed in Japanese Patent No. 3320954 is difficult to downsize, and particularly the full-color image forming apparatus having plural image forming units are more difficult to downsize.
As one of the methods of downsizing the image developer, the developer storing part is located above the developer charging and layer forming part, i.e., the image developer becomes vertically long. The developer is fed in the direction of gravitational force and an intake capacity of the developer varies a feeding amount thereof and it is difficult to stably feed the developer, resulting in foggy images due to an excessive uncharged developer and defective images such as image density variation.
Further, the toner has smaller particle diameter recently in order to produce high-quality images has higher cohesion. When the apparatus is not used or left for a while, the developer in the image developer agglutinates due to gravity and only the toner very close to the feeding roller and developing roller is used, resulting in image density deterioration and hazy images due to poor feeding of the toner.
Constantly stirring the whole toner in the image developer is considered to prevent the toner cohesion due to gravity. However, the toner is difficult to transfer up and down in the vertically long image developer, the toner is unnecessarily stressed and deterioration thereof is accelerated, and the toner circulation close to the feeding roller deteriorates occasionally depending on the stirring direction.
Japanese Published Unexamined Patent Application No. 2003-5487 divides the vertically long image developer into the above and below, detects a toner amount of the below and controls a rotation of a toner feeding member such that the toner is difficult to pressurize the feeding roller neighborhood. However, 4 sets of parts such as a toner amount detector (sensor) and an electromagnetic clutch controlling the rotation of the toner feeding member are required, resulting in complicated apparatus and cost increase.
Japanese Published Unexamined Patent Application No. 2001-194883 discloses means of reducing toner stress by reducing stress to the developing roller, doctor blade and feeding roller. However, stress is directly applied thereto unchangeably and the developer having a small particle diameter and low-temperature fixability is not affected thereby. Under an environment of high temperature and high humidity, image density deterioration and hazy images due to deterioration of fluidity are inevitable.
Because of these reasons, a need exists for a downsized image developer longitudinally having a developer container above a developer charging and layer forming part thereof, capable of stably feeding a developer to the developer charging and layer forming part to develop quality images.